The present invention relates to a rolling mill, particularly to the type employed to roll flat metal products, such as steel strips. Mills of this type may be provided with roll shifting mechanisms for axially moving the rolls in opposite directions to either prevent objectional roll wear caused by the edges of the strips during rolling or to aid in profile and shape control of the strips during rolling. Roll shifting is presently provided in mills having different numbers of rolls, but is more commonly found in 4 Hi, 5 Hi and 6 Hi mills. For simplicity in explaining the present invention, the invention will be considered in terms of a 4 Hi mill, but it will be understood to be equally applicable to other types of mills having generally similar structures and objectives.
In the past, 4 Hi mills having work roll shifting have generally incorporated two different designs with reference to the roll balance and roll bending piston cylinder assemblies provided to maintain the upper work roll away from the lower work roll when no strip is between the rolls and for exerting a positive or negative force in the vertical direction of the rolling force to aid in shape or profile strip control. The number of cylinders may consist of a single cylinder or one or two pairs per bearing chock and in some cases four pairs, in which in certain cases the pairs are spaced on either side of the axis of the work rolls.
In some of these designs the cylinder or cylinders are mounted in one of the bearing chocks of each pair so as to exert their forces on the other cooperative bearing chock of the work rolls. In this design while the shifting of the rolls does not disturb the fixed relationship between the cylinders and bearings of the rolls, since they move as a unit which is an important advantage in view of the fact that there is no change in the lever arm effect between the cylinders and the roll, it has several serious disadvantages which may be briefly identified is follows: (a) it requires that the usually large number of spare bearing chocks be provided with machined openings for the cylinders. (b) it requires the need of maintenance personnel to connect and disconnect the hydraulic lines during roll changing, and (c) to accommodate roll shifting, it requires providing flexible hoses for the hydraulic lines with all their attending disadvantages.
In the second design the cylinders are mounted in nonmoveable blocks provided in the window of each housing, i.e. the housings are Mae West housings, and exert their forces on both of the opposite pairs of bearing chocks at each roll end, which design eliminates each of the aforesaid enumerated disadvantages. However, since in the latter design during roll shifting the rolls with their bearing chocks move relative to the stationary mounted cylinders, unless compensated for there is created a change in the lever arm effect noted above resulting in an undesirable character of loading of the work roll bearings leading to premature bearing failure.
Most of the above noted characteristics and components are illustrated and in some cases more fully described in the following U.S. Patents: Pat. No. 3,593,554 dated July 20, 1971, Pat. No. 3,857,268 dated Dec. 31, 1974, Pat. No. 4,369,646 dated Jan. 25, 1983, Pat. No. 4,543,810 dated Oct. 1, 1985, and Pat. No. 4,711,116 dated Dec. 8, 1987.